Heteroepitaxy, i.e., the epitaxial growth of a layer of material on a substrate that differs in chemical composition from the epitaxial layer, has been a field of active research for some time. These efforts have led to some technologically important applications. For instance, III-V or II-VI semiconductors have been combined with ternary materials in heteroepitaxialr systems. Exemplary of this application is the system GaAs/Al.sub.x Ga.sub.1-x As that is widely used in optoelectronic devices. Patterned monocrystalline layers of III-V compounds have also been grown on III-V substrates (U.S. Pat. No. 3,928,092, issued Dec. 23, 1975 to W. C. Ballamy et al). Semiconductor layers are also being grown epitaxially on insulators. An example of such a heteroepitaxial system of technological importance is silicon on sapphire. Similarly, compound semiconductors, especially the III-V compounds, have been grown on sapphire substrates. For a general review, see, for instance, Heteroepitaxial Semiconductors for Electronic Devices, G. W. Cullen and C. C. Wang, editors, Springer-Verlag, New York (1978).
Despite the efforts of the last years, the number of heteropitaxial systems that have been developed sufficiently to permit device application is small. In particular, the number of demonstrated heteroepitaxial structures comprising an epitaxial metal layer is at present very limited. However, such systems not only are necessary for making three-dimensional integrated circuits, but would permit the realization of novel device structures, e.g., a metal-base transistor. Chief among the reported heterostructures containing an epitaxial metal layer are CoSi.sub.2 on Si, and NiSi.sub.2 on Si.
When CoSi.sub.2 or NiSi.sub.2 epitaxial films are grown on Si(111) by one of the techniques that have been employed successfully to date, e.g., by low temperature metal deposition and high temperature reaction, or by molecularbeam epitaxy, it has been found that the epitaxial material formed often contains two types of crystallites. Both types share the surface normal [111] direction with the substrate, but one has an orientation that is rotated by 180 degrees about the normal, as compared to the substrate, and the other has an orientation that is identical to that of the substrate. The former will be referred to herein as "type B", and the latter as "type A". When grains of both orientations are present in epitaxial material then the total amounts of each are often similar. The grains, of course, are separated by high-angle grain boundaries, which contribute significantly to electron scattering in the material, thus reducing the usefulness of such material as contact material in Very Large Scale Integration (VLSI) semiconductor devices. Furthermore, a silicide layer containing both A and B type crystallites is typically unsuitable to serve as substrate layer for the growth of subsequent device-quality heteroepitaxial material, e.g., a further Si layer, as would be required in the manufacture of three-dimensional integrated circuits.
Although epitaxial layers of CoSi.sub.2 and NiSi.sub.2 have recently been grown on Si(111), single crystal NiSi.sub.2 could not be grown on Si(100), due to [111] faceting of the NiSi.sub.2 /Si interface. K. C. Chiu et al, Applied Physics Letters, Vol. 38, pp. 988-990, (1981). Epitaxial growth of high quality single crystal metal silicide on Si(100) is, however, of great technological interest since current silicon technology uses almost exclusively (100)-oriented material.
Silicide-silicon heterostructures and a technique for preparing these structures have been disclosed by J. C. Bean et al in a U.S. patent application, Ser. No. 156,649, filed June 5, 1980. The technique disclosed therein comprises exposing a single-crystal silicon substrate to a vapor comprising a silicide-forming metal, while maintaining the substrate at an appropriate temperature at which the metal reacts, in situ, with the silicon to form a metal silicide single crystal. The heteroepitaxial silicide layers formed by this technique typically are of high perfection, as determined by Rutherford backscattering spectroscopy (RBS) and channeling, and by transmission electron microscopy.
Because of the great technological promise of heteroepitaxially grown layers of material of device quality, and because of the limited number of systems in which such growth has been achieved so far, a broadly applicable method for growing such layers if of substantial interest. In particular, a method for growing substantially perfect metal silicide on silicon is of great interest to the semiconductor industry. And furthermore, a growth technique that permits control of the orientation of the epitaxial material formed is of added technological and scientific significance.